Solid polymer electrolyte fuel cell system with ribbed configuration

ABSTRACT

In a solid electrolyte polymer fuel cell system, a fuel cell includes ribs integrally formed with an anode or an anode chamber, ribs integrally formed with a cathode or cathode chamber, and a water distributor. The water distributor may be a beam provided with slits, an electroconductive body, a wick, or a combination of the beam with slits and a hydrophilic body. Fuel gas and water distributed by the water distributor are passed through the ribs of the ribbed anode or ribbed anode chamber to provide sufficient hydrogen ions and water of inclusion with the solid polymer electrolyte. Oxidizer gas and water to be discharged are passed through the ribs of the ribbed cathode or ribbed cathode chamber. Water is discharged efficiently.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid polymer electrolyte fuel cellsystem and more particularly to an improved fuel cell structure andmethod for feeding water of inclusion in a solid polymer electrolytemembrane and for feeding reaction gases for the fuel cell system.

2. Description of Prior Art

Fuel cells are roughly classified into two groups, for example, lowtemperature-operating ones such as an alkali type, a solid polymerelectrolyte type, and a phosphoric acid type, and hightemperature-operating ones such as a molten salt type, and a solid oxideelectrolyte type.

Solid polymer electrolyte type fuel cells have a solid polymerelectrolyte membrane having two main surfaces provided with an anode anda cathode, respectively, and an electrode substrate, the anode andcathode being sandwiched by the solid polymer electrolyte and therespective electrode substrates. As the solid polymer electrolytemembrane, there have been used polystyrene cation exchange resins havinga sulfonic acid group as cationic electroconductive membranes,fluorocarbon sulfonic acid/polyvinylidene fluoride mixed membranes, ormembranes composed of a fluorocarbon matrix and trifluoroethylenegrafted thereto.

Recently, fuel cells with a prolonged service life by the use ofperfluorocarbonsulfonic acid membrane (Nafion, trade name for a productby DuPont de Nemours, Ill. U.S.A.) have been put on the market. Solidpolymer electrolyte membranes have proton (hydrogen ion) exchange groupsin their molecule and have resistivities not higher than 20 Ω·cm at roomtemperature when hydrated to saturation, thus acting as aproton-conductive electrolyte. Saturated water content varies reversiblydepending on the temperature of the membrane.

An electrode substrate, which is made of a porous material, acts as ameans for supplying a reaction gas to a fuel cell and also as acollector. In anodes or cathodes, there are formed three phase zoneswhere electrochemical reactions takes place.

In an anode, there occurs the following reaction:

    H.sub.2 →2H.sup.+ +2e.sup.-                         ( 1)

In a cathode, what occurs is the following reaction:

    1/2O.sub.2 +2H.sup.+ +2e.sup.- →H.sub.2 O           (2)

In other words, in the anode, hydrogen supplied from outside of thesystem produces protons (H⁺) and electrons (e⁻). Protons producedmigrate through the ion exchange membrane toward the cathode whereaselectrons migrate into the cathode through an external circuit connectedthereto. On the other hand, in the cathode, oxygen supplied from outsideof the system, protons which have migrated through the ion exchangemembrane and electrons transferred through the external circuit react toproduce water (H₂ O).

In this type of solid polymer electrolyte fuel cells, protons migratefrom the anode to the cathode through the ion exchange membrane in ahydrated state, resulting in that the water content of the membrane inthe vicinity of the anode decreases and the ion exchange membrane tendsto be dried. Hence migration of protons becomes difficult in thevicinity of the anode unless water is supplied thereto. On the otherhand, in the cathode, water is produced as shown by formula (2) above.However, generally solid polymer electrolyte fuel cells are operated attemperatures not higher than 100° C., which means that water produced onthe cathode side is considered to be in a liquid state. Therefore, inthe cathode, excess amounts of water accumulate since water is not onlyfreshly produced as a result of electrode reaction but also releasedfrom hydrated protons due to disappearance of the protons in thereaction on the cathode. The water which has accumulated would fill andclog pores in the electrode substrate to inhibit diffusion of thereaction gas therethrough.

Accordingly, in order to operate a solid polymer electrolyte fuel cellcontinuously and efficiently, it is necessary to properly supply waterto the anode to replenish water of inclusion contained by the solidpolymer electrolyte membrane and discharge the water which has migratedtherefrom and accumulated in the cathode. For optimizing the watercontent of the ion exchange membrane, the water of inclusion in the ionexchange membrane has conventionally been replenished by bubbling thefuel gas into water kept at a temperature higher than the temperature atwhich the fuel cell is operated to humidify the fuel gas and supplyingthe gas thus humidified to the anode side of the fuel cell. On the otherhand, the water which accumulated in the cathode has conventionally beendischarged by supplying a large amount of dry oxidizer gas to thecathode of the fuel cell, or by cooling steam formed in the cathode tocondense it and discharging the resulting water to outside the system.

However, the conventional method in which water in the form of steam issupplied to the ion exchange membrane to replenish therewith the waterof inclusion in the membrane has some problems. For example, theconventional method does not supply an amount of water which is enoughto replenish the water which has migrated due to hydration because watercondenses in the inside of the ion exchange membrane in an amount whichcorresponds to the difference between the saturation vapor pressure ofthe reaction gas at a humidification temperature and the saturationvapor pressure at a cell operation temperature. Thus, it is generallydifficult to use a large difference between the humidificationtemperature and the cell operation temperature. Further, use ofincreased humidification temperatures leads to an increase in thepartial pressure of aqueous vapor (0.47 atm at 80° C.; 0.69 atm at 90°C.) to thus decrease the partial pressure of the fuel gas. As a result,supply of the fuel gas decreases to deteriorate the characteristics ofthe fuel cell.

SUMMARY OF THE INVENTION

An object of the present invention is to overcome the aforementionedproblems involved in the prior art and provide a solid polymerelectrolyte fuel cell system in which fuel gas and water forreplenishing water of inclusion contained in the solid polymerelectrolyte membrane are supplied to the anode with sufficientefficiency and which has a high current-voltage characteristics.

Another object of the present invention is to provide a method forsupplying fuel gas and water for replenishing water of inclusioncontained by a solid polymer electrolyte membrane in which water issupplied in a liquid state in order to supply fuel gas at a high partialpressure without being adversely influenced by the partial pressure ofaqueous vapor.

Still another object of the present invention is to provide a solidpolymer electrolyte fuel cell system and a method for supplying fuel gasand water for replenishing water of inclusion contained in a solidpolymer electrolyte membrane in which water is supplied withoutinhibiting the flow of reaction gases.

As a result of extensive investigations by the present inventors, it hasnow been found that the aforementioned objects can be achieved by theprovision of rib means in the anode chambers and cathode chambers, andalso a water distribution means in the anode chamber. The presentinvention is based on this discovery.

In the first aspect of the present invention, a solid polymerelectrolyte fuel cell system comprises:

a solid polymer electrolyte membrane;

an anode chamber arranged in contact with the solid polymer electrolytemembrane;

a cathode chamber arranged in contact with the solid polymer electrolytemembrane, the cathode chamber and the anode chamber sandwichingtherebetween the solid polymer electrolyte membrane;

a ribbed anode arranged in the anode chamber and having a first surfaceprovided with a plurality of first ribs defining a plurality of firstgrooves and a second surface which is flat and in contact with the solidpolymer electrolyte membrane;

a ribbed cathode arranged in the cathode chamber and having a firstsurface provided with a plurality of second ribs defining a plurality ofsecond grooves and a second surface which is flat and in contact withthe solid polymer electrolyte membrane;

a water feed pipe for feeding water connected to the anode chamber;

a fuel gas feed pipe connected to the anode chamber and feeding a fuelgas;

a water distribution means for distributing water fed from the waterfeed pipe to the plurality of first ribs, the water distribution meansbeing arranged in the anode chamber;

a first discharge pipe connected to the anode chamber and discharging anunused fuel gas and water; and

an oxidizer gas feed pipe connected to the cathode chamber and feedingan oxidizer gas;

a second discharge pipe connected to the cathode chamber and dischargingan unused oxidizer gas and water;

whereby the fuel gas passes in the first grooves and the oxidizer gaspasses in the second grooves.

Here, the water distribution means may comprise a beam arranged abovethe ribbed anode and provided with a restricted passage through whichthe water from the water feed pipe flows down.

The water distribution means may comprise an electroconductive porousbody arranged in contact with the first surface of the ribbed anode.

The water distribution means may comprise a network composed of a wickarranged along and between the first ribs of the ribbed anode.

The water distribution means may comprise a beam arranged above theribbed anode and provided with a restricted passage through which waterflows down and a hydrophilic band arranged along and embedded in thefirst ribs of the ribbed anode.

In the second aspect of the present invention, a solid polymerelectrolyte fuel cell system comprises:

a solid polymer electrolyte membrane;

a ribbed anode chamber arranged in contact with the solid polymerelectrolyte membrane and having a first surface provided with aplurality of first ribs defining a plurality of first grooves;

a cathode chamber arranged in contact with the solid polymer electrolytemembrane and having a first surface provided with a plurality of secondribs defining a plurality of second grooves, the cathode chamber and theanode chamber sandwiching therebetween the solid polymer electrolytemembrane;

an anode arranged in the anode chamber having a first surface which isflat and in contact with the solid polymer electrolyte membrane, and asecond surface which is flat and in contact with the first ribs of theribbed anode chamber;

a cathode arranged in the cathode chamber and having a first surfacewhich is flat and in contact with the solid polymer electrolyte membraneand a second surface which is flat and in contact with the second ribsof the ribbed cathode chamber;

a water feed pipe for feeding water connected to the ribbed anodechamber;

a fuel gas feed pipe connected to the ribbed anode chamber and feeding afuel gas;

a water distribution means for distributing water fed from the waterfeed pipe to the plurality of first ribs of the ribbed anode chamber,the water distribution means being arranged in the ribbed anode chamber;

a first discharge pipe connected to the ribbed anode chamber anddischarging an unused fuel gas and water; and

an oxidizer gas feed pipe connected to the ribbed cathode chamber andfeeding an oxidizer gas;

a second discharge pipe connected to the ribbed cathode chamber anddischarging an unused oxidizer gas and water;

whereby the fuel gas passes in the first grooves and the oxidizer gaspasses in the second grooves.

Here, the water distribution means may comprise a beam arranged in anupper portion of the ribbed anode chamber and provided with a restrictedpassage through which the water from the water feed pipe flows down.

The water distribution means may comprise an electroconductive porousbody provided in the first ribs of the ribbed anode chamber.

The water distribution means may comprise a network composed of a wickarranged along and between the first ribs of the ribbed anode chamber.

The water distribution means may comprise a beam having a restrictedpassage for water and a hydrophilic band arranged along and embedded inthe first ribs of the ribbed anode chamber.

In the third aspect of the present invention, a method for feeding waterof inclusion contained in a solid polymer electrolyte membrane and gasesin a solid polymer electrolyte fuel cell system having a solid polymerelectrolyte membrane, an anode chamber, a cathode chamber, an anode, anda cathode, the anode chamber and cathode chamber sandwiching the solidpolymer electrolyte membrane, comprises the steps of:

providing an anode chamber including a ribbed anode having a firstsurface provided with a plurality of first ribs defining first groovesand a second surface, opposite to the first surface, being flat and incontact with the solid polymer electrolyte membrane, a ribbed cathodehaving a first surface provided with a plurality of second ribs definingsecond grooves and a second surface, opposite to the first surface,being flat and in contact with the solid polymer electrolyte membraneand a water distribution means in the anode chamber;

passing a fuel gas through the first grooves;

passing water through the water distribution means to distribute waterin the first ribs;

discharging an unused portion of the fuel gas and an excess portion ofthe water through a first discharge pipe;

passing an oxidizer gas through the second grooves to the cathode toproduce water; and

discharging the water produced in the cathode and an unused portion ofthe oxidizer gas.

Here, the water distribution means may comprise a beam arranged abovethe ribbed anode and provided with a restricted passage through whichthe water flows down.

The water distribution means may comprise an electroconductive porousbody arranged in contact with the first surface of the ribbed anode.

The water distribution means may comprise a network composed of a wickarranged along and between the first ribs of the ribbed anode.

The water distribution means may comprise a beam arranged above theribbed anode and provided with a restricted passage through which waterflows down and a hydrophilic band arranged along and embedded in thefirst ribs of the ribbed anode.

In the fourth aspect of the present invention, a method for feedingwater of inclusion contained in a solid polymer electrolyte membrane andgases in a solid polymer electrolyte fuel cell system having a solidpolymer electrolyte membrane, an anode chamber, a cathode chamber, ananode, and a cathode, the anode chamber and cathode chamber sandwichingthe solid polymer electrolyte membrane, comprises the steps of:

providing a ribbed anode chamber including an anode, the ribbed anodechamber having a plurality of first ribs defining a plurality of firstgrooves, the first ribs opposing the solid polymer electrolyte membranevia the anode, a ribbed cathode having a plurality of second ribsdefining a plurality of second grooves, the second ribs opposing thesolid polymer electrolyte membrane via the cathode, and a waterdistribution means in the anode chamber;

passing a fuel gas through the first grooves;

passing water through the water distribution means to distribute waterin the first ribs;

discharging and unused portion of the fuel gas and an excess portion ofthe water through a first discharge pipe;

passing an oxidizer gas through the second grooves to the cathode toproduce water; and

discharging the water produced in the cathode and an unused portion ofthe oxidizer gas.

Here, a beam may be arranged above the ribbed anode, a restrictedpassage may be formed in the beam, and the water may be passed throughthe restricted passage to the first ribs of the ribbed anode chamber.

An electroconductive porous body having a plurality of ribs may beprovided, and the water may be passed through the ribs of theelectroconductive porous body.

A wick in the form of a network may be provided along and between thefirst ribs of the ribbed anode chamber, and water may be passed throughthe wick.

A beam may be provided above the ribbed anode, a restricted passagethrough which water flows down, a hydrophilic band may be arranged alongand embedded in the first ribs of the ribbed anode chamber.

According to the present invention, the fuel gas and the water from thewater distribution means flow well in the rib means in the form of ribsin a ribbed anode or in the form of a ribbed anode chamber tosufficiently diffuse the fuel gas and water in pores in the ribbed anodeor L-form bores. The water is uniformly distributed in respective ribsin the ribbed anode or anode chamber to form a unique flow of water. Thewater which flows down through a plurality of restricted passagesprovided in a horizontal beam in the anode chamber flows on respectivesurfaces of the ribs of the ribbed anode or anode chamber which surfacescorrespond to the restricted passages. Fuel gas flows on other surfacesof the ribs of the ribbed anode or anode chamber. When anelectroconductive porous material is used as the water distributionmeans or water distributor, the water migrates into theelectroconductive porous material as a result of capillary action, whichgives similar effects to those of water flowing on the surfaces of theribs of the ribbed anode or anode chamber. The water migrates through awick due to capillary action and thus the water can flow through anetwork composed of a wick. In the case of the combination of ahorizontal beam with restricted passages and hydrophilic bands, thewater flows through respective restricted passages of the horizontalbeam onto the underlying hydrophilic bodies or bands, and then the waterflows along and inside the ribs of the ribbed anode or anode chamber.When it has reached the anode the water is taken up as water ofinclusion by the ion exchange membrane while the fuel gas which hasreached the anode is dissociated to give protons (H⁺). In this manner,the water for replenishing the water of inclusion in the ion exchangemembrane is supplied in a liquid state so that the fuel gas can besupplied at a high partial pressure without adverse influences from thepartial pressure of aqueous vapor. As a result the ion exchange membranecan be maintained always in a sufficiently wet state, so that itsresistance polarization can be maintained at a low level. Utilization ofthe fuel gas at a high concentration reduces concentration polarization.These features, together with good flow of oxidizer gas and water in theribs of the ribbed cathode or cathode chamber, give a basis of improvedpolarization characteristics of the solid polymer electrolyte fuel cellsystem of the present invention.

Flow of the oxidizer gas and water through the ribs of the ribbedcathode or cathode chamber is substantially the same as in the case offlow of the fuel gas and water through the ribs of the ribbed anode oranode chamber.

While the present invention is applied typically to a hydrogen-oxygenfuel cell it can also be applied to other types of fuel cell systems,such as one using methanol gas as the fuel gas, so far as replenishmentof water of inclusion contained in the solid polymer electrolytemembrane is necessary or effective.

The above and other objects, effects, features and advantages of thepresent invention will become more apparent from the followingdescription of embodiments thereof taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially cross sectioned schematic view showing a solidpolymer electrolyte fuel cell system according to Embodiment 1 of thepresent invention;

FIG. 2 is an exploded perspective view showing the interior of an anodechamber in the solid polymer electrolyte fuel cell system shown in FIG.1;

FIG. 2A is an exploded perspective view partially showing the interiorof a cathode chamber in the solid polymer electrolyte fuel cell systemof FIG. 1;

FIG. 3 is an exploded perspective view showing the interior of a anodechamber in a solid polymer electrolyte fuel cell system according toEmbodiment 2 of the present invention;

FIG. 4 is a perspective view showing a combination of a ribbed anode anda network composed of a wick in a solid polymer electrolyte fuel cellsystem according to Embodiment 3 of the present invention;

FIG. 5 is a perspective view showing a combination of a ribbed anode anda hydrophilic band in a solid polymer electrolyte fuel cell systemaccording to Embodiment 4 of the present invention;

FIG. 6 is a graph illustrating characteristics of the fuel cellsaccording to Embodiments 1 to 4 according to the present invention ascompared with the characteristics of a conventional fuel cell system;

FIG. 7 is a partially cross sectioned schematic view showing a solidpolymer electrolyte fuel cell system according to Embodiment 5 of thepresent invention;

FIG. 8 is an exploded perspective view showing the interior of a ribbedanode chamber in the solid polymer electrolyte fuel cell system shown inFIG. 7;

FIG. 8A is an exploded perspective view partially showing the interiorof a ribbed cathode chamber in the solid polymer electrolyte fuel cellsystem of FIG. 7;

FIG. 9 is an exploded perspective view showing the interior of a ribbedanode chamber in a solid polymer electrolyte fuel cell system accordingto Embodiment 6 of the present invention;

FIG. 10 is a perspective view showing a combination of ribs of a ribbedanode chamber and a network composed of a wick in a solid polymerelectrolyte fuel cell system according to Embodiment 7 of the presentinvention; and

FIG. 11 is a perspective view showing a combination of ribs of a ribbedanode chamber and a hydrophilic band in a solid polymer electrolyte fuelcell system according to Embodiment 8 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in greater detailwith reference to some embodiments thereof which should not be construedas limiting the present invention thereto in any manner.

Embodiment 1

FIG. 1 is a partially cross sectioned schematic view showing a solidpolymer electrolyte fuel cell system according to Embodiment 1. FIG. 2is an exploded perspective view showing the interior of the anodechamber in the SPE fuel cell shown in FIG. 1, and FIG. 2A is an explodedpartial perspective view showing the interior of a cathode chamber inthe solid polymer electrolyte fuel cell system of FIG. 1, with a feedpipe and a second discharge pipe being omitted. As shown in FIG. 1, asolid polymer electrolyte fuel cell system 20 includes a fuel cell 22,which includes a solid polymer electrolyte membrane 24, an anode chamber26 and a cathode chamber 28, the anode and cathode chambers 26 and 28sandwiching therebetween the SPE membrane 24. The anode chamber 26contains a ribbed anode 30 having a plurality of ribs 32 parallel toeach other and arranged generally vertically, and a beam 36 above theribbed anode 30. The beam 36 is arranged substantially horizontally inthe upper space at proper distances from an upper inner surface of theanode chamber and from respective upper ends of the ribs 32 of theribbed anode 30. The horizontal beam 36 is formed integrally with theanode chamber 26. The beam 36 has a plurality of restricted passages 37each in the form of a slit through which water can flow down. Therespective positions of the slits 37 correspond to side surfaces 32c ofthe ribs 32, the side surfaces 32c being perpendicular to the sidesurfaces of the ribs 32 opposing the inner side surface 26a of the anodechamber.

The cathode chamber 28 (FIG. 2A) contains a ribbed cathode 50 having aplurality of ribs 52 parallel to each other and arranged generallyvertically. The ribbed anode 30 (FIG. 2) has a first surface 30', whichis flat and arranged on the side of the SPE membrane 24, and a secondsurface, on which the ribs 32 are formed integral to the anode and whichis arranged on the gas side or the side opposing an inner side surface26a of the anode chamber 26. Similarly, the ribbed cathode 50 has afirst surface 50', which is flat and arranged on the side of the SPEmembrane, and a second surface, on which the ribs 52 are formed integralto the cathode and which is arranged on the gas side or the sideopposing an inner side surface of the cathode chamber 28. The firstsurfaces (flat surfaces) of the anode and cathode are coated with aplatinum catalyst layer (not shown) and these first surfaces are pressedagainst the SPE membrane 24. Reaction gases (a fuel gas and an oxidizergas) fed through feed pipes 38 and 56, respectively, flow throughvertical grooves 34 and 54, respectively, defined by the ribs 32 and 52of the ribbed anode 30 and ribbed cathode 50, respectively, togetherwith the inner side surfaces of the anode and cathode chambers 26 and28, respectively. Water in a liquid state is fed through a water feedpipe 40, separately from the fuel gas feed pipe 38, from a waterreservoir 42 by a pump 44 and introduced into the anode chamber 26, andseparated into a discharge water and a discharge fuel gas (unused)through a first discharge pipe 46. The separated water is fed back tothe water reservoir 42, and recycled.

The water which flows into the anode chamber 26 from the water feed pipe40 passes through slits 37 of the horizontal beam 36. The aforementionedposition of the slits 37 makes it possible for water to flow down alongthe side surfaces 32c of the first rib elements. The restricted passages37 may be of any other form, e.g., a plurality of perforations arrangedin a line so far as such can provide a restricted downward flow ofwater. Since the amount of the water which flows through the slits 37 issmall or restricted, the water flows down along the side surfaces of thegroove defined by the ribs 32 and the anode but does not fill or closethe grooves (or ducts when taken together with the inner side surface ofthe anode chamber), with the result that flow of the fuel gas is notprevented. The water which is flowing down is partly absorbed by theribbed anode 30 and migrates into the SPE membrane 24. The portion ofthe water which has not been absorbed reaches the bottom of the anodechamber and combined there, and then discharged through the firstdischarge pipe 46. An oxidizer gas is fed to the cathode chamber 28through an oxidizer gas feed pipe 56 and passes through the ribs 52 ofthe ribbed cathode 50. The oxidizer gas is used in the electrodereaction which takes place in a three phase zone formed between thecathode and the SPE membrane to produce water. Unused portion of theoxidizer gas together with wter produced (including water derived fromhydration water in hydrated protons) is discharged through a seconddischarge pipe 58. A platinum catalyst layer (not shown) is providedbetween the ribbed cathode 50 and the SPE membrane 24. The structure ofthe ribbed cathode 50 may be substantially the same as the ribbed anode30.

EMBODIMENT 2

FIG. 3 is an exploded perspective view showing the interior of an anodechamber in the solid polymer electrolyte fuel cell system according toEmbodiment 2. As shown in FIG. 3, an anode chamber 26A is providedtherein with an electroconductive porous plate 36A instead of thehorizontal beam 36 with slits 37 used in Embodiment 1 (FIG. 2). Theelectroconductive porous plate 36A contacts ribs 32A of a ribbed anode30A. The height of the porous plate 36A is such that its top end is justbelow a water feed pipe 40 connected to an upper part of the anodechamber. The thickness of the porous plate 36A is set such that sum ofthe thickness, x₁, of a portion of the ribbed anode 30A where one of theribs 32A is present and the thickness, x₂, of the porous plate 32A isequivalent to the depth, x, of the anode chamber 26A.

Water is supplied on the top end of the porous plate 36A, and spreadsthrough the entire porous plate. A portion of the water suppliedmigrates from the plate 36A to the SPE membrane 24 through the ribs 32Aof the ribbed anode 30A, and is absorbed by the membrane. Excessivewater (unabsorbed portion) transudes from a lower end of the porousplate 36A, and discharged together with unused fuel gas through thefirst discharge pipe 46. Suitably the electroconductive porous plate 36Ais made of a metal. Also, woven or nonwoven fabrics of carbon may beused as the porous material.

Embodiment 3

FIG. 4 is a perspective view showing a combination of a ribbed anode anda wick in a solid polymer electrolyte fuel cell system according toEmbodiment 3. A ribbed anode 30B is provided with horizontal grooves andvertical grooves to form many island-like isolated protrusions or ribs32B. A wick 36B is provided around the respective ribs 32B to form anetwork. An upper end 36B' of the wick may be arranged in the vicinityof an opening of the water feed pipe 40 (FIG. 3) in the anode chamber26A (FIG. 3). Water supplied through the water feed pipe 40 (FIG. 3)penetrates or passes through the wick and migrates to the ribbed anode30B through the ribs 32B, and is absorbed by the SPE membrane 24 (FIG.1). Unabsorbed water or excessive water transudes from a lower end 36B"of the wick, and is discharged through the first discharge pipe 46 (FIG.3) together with unreacted fuel gas. The wick is made of fine threads ofa fibrous material preferably selected from various natural fiber,synthetic fiber or metallic fiber, the fine threads having been twistedtogether.

Embodiment 4

FIG. 5 is a perspective view showing a combination of a ribbed anode anda hydrophilic band in a solid polymer electrolyte fuel cell systemaccording to Embodiment 4. A ribbed anode 30C has a plurality ofintegral ribs 32C vertically arranged and parallel to each other todefine a groove 34C between any two adjacent ribs 32C. A hydrophilicband 36C is provided in every other groove 34C. The width, w₁, of therib 32C is made somewhat smaller than the thickness, w, of the anode 30in FIG. 2. In the instant embodiment, the sum of the width, w₂, of thehydrophilic band 36C and the widths, w₁ and w₁, of two ribs 32Csandwiching the hydrophilic band may be set equivalent to w. Usually,the distance, d₁, between two adjacent ribs 32C defining a groove 34Cwithout the hydrophilic band 36C may be different from (larger than) thedistance, d₂ (d₂ =w₂), between two adjacent rib potions 32C defining agroove 34C' stuffed with the hydrophilic band 36C. However, it is alsopossible to provide the ribs 32C at the same pitch and fill thehydrophilic band 36C in every other groove defined by the ribs. Waterfed from the water feed pipe 40 (FIG. 2) flows down through a horizontalbeam of the same structure as the horizontal beam 36 having slits 37shown in FIG. 2 and distributes to a plurality of the hydrophilic bands36C. A portion of the water supplied migrates from the hydrophilic bands36C to the ribs 32C sandwiching the respective hydrophilic bands, and isabsorbed by the SPE membrane 24 (FIG. 1). Excessive water transudes fromrespective lower ends of the hydrophilic bands 36C, and is dischargedthrough the first discharge pipe 46 (FIG. 2). The hydrophilic band 36Cmay be a rod of a porous metal, a felt or a twisted yarn.

FIG. 6 is a graph illustrating characteristics of the fuel cellsaccording to Embodiments 1 to 4 of the present invention as comparedwith the characteristics of a conventional fuel cell system. In thegraph the horizontal axis indicates current density (A/cm²) and thevertical axis indicates terminal voltage. The water of inclusioncontained in the ion exchange membrane used is supplied in a liquidstate and therefore the ion exchange membrane (SPE membrane) ismaintained always in a sufficiently wet state, thus decreasingresistance polarization. Since the fuel cell systems of the presentinvention enable supply of the fuel gas at a high concentration,concentration polarization decreases. Therefore, according to thepresent invention a solid polymer electrolyte fuel cell system havingimproved polarization characteristics can be obtained.

Embodiment 5

FIG. 7 is a partially cross sectioned schematic view showing a solidpolymer electrolyte fuel cell system according to Embodiment 5. FIG. 8is an exploded perspective view showing the interior of a ribbed anodechamber in the solid polymer electrolyte fuel cell system shown in FIG.7. FIG. 8A is an exploded perspective view showing the interior of aribbed cathode chamber in the solid polymer electrolyte fuel cell systemshown in FIG. 7, with a feed pipe and a second discharge pipe beingomitted. As shown in FIG. 7, an SPE fuel cell system 100 comprises afuel cell 122 which includes an SPE membrane 124, a ribbed anode chamber126 and a ribbed cathode chamber 128, the ribbed anode chamber 126 andthe ribbed cathode chamber 128 sandwiching therebetween the SPE membrane124. The ribbed anode chamber 126 and the ribbed cathode chamber 128contain an anode 130 and a cathode 150, respectively. The anode andcathode are made of a porous carbon plate and coated with a platinumcatalyst (not shown), and are pressed against the SPE membrane 124.

The ribbed anode chamber 126 has a plurality of ribs 132. The ribs 132are parallel to each other and vertical, and define grooves 134 betweenany adjacent two of them. The ribs 132 are integral to a rib substrate133 connected or integral to an inner side surface of the ribbed anodechamber opposing the SPE membrane 124. The ribbed cathode chamber 128has a plurality of ribs 152 which may be of the same structure as theribs 132 of the ribbed anode chamber 126, defining grooves 154 betweenany adjacent two thereof. Reaction gases (a fuel gas and an oxidizergas) fed through gas feed pipes 38 and 56, respectively, flow throughthe vertical grooves 134 and 154, respectively, defined by the ribs 132and 152 of the ribbed anode chamber 126 and the ribbed cathode chamber128, respectively, together with the inner side surfaces of the anodeand cathode chambers 126 and 128, respectively. Water in a liquid stateis fed through a water feed pipe 40, separately of the fuel gas feedpipe 38, from a water reservoir 42 by a pump 44 and introduced into theanode chamber 126, and separated into a discharge water and a dischargefuel gas (unused). The separated water is fed back to the waterreservoir 42, and recycled.

The water which flows into the anode chamber 126 from the water feedpipe 40 passes through slits 137 of a horizontal beam 136. Theconstruction of the horizontal beam 136 having slits 137 issubstantially the same as the horizontal beam 36 with slits 37 shown inFIG. 2. Since the amount of the water which flows through the slits 137is small or restricted, the water flows down along the side surfaces ofthe groove defined by the ribs 132 and the anode but does not fill orclose the grooves (or ducts when taken together with the inner sidesurface of the anode chamber), with the result that the flow of the fuelgas is not prevented. The water which is flowing down is partly absorbedby the ribs 132 of the ribbed anode 126 and migrates into the anode andthen to the SPE membrane 124. The portion of the water which has notbeen absorbed reaches the bottom of the ribbed anode chamber and iscombined there, and then discharged through the first discharge pipe 46.An oxidizer gas is fed to the ribbed cathode chamber 128 through anoxidizer gas feed pipe 56 and passes through the ribs 152 of the ribbedcathode chamber 128. The oxidizer gas is used in the electrode reactionwhich takes place in a three phase zone formed between the cathode andthe SPE membrane to produce water. Unused portion of the oxidizer gastogether with water produced (including water derived from hydrationwater in hydrated protons) is discharged through a second discharge pipe58. A platinum catalyst layer (not shown) is provided between the ribbedcathode 150 and the SPE membrane 124. The structure of the ribbedcathode chamber 128 containing the ribs 152 may be substantially thesame as the ribbed anode chamber 126 containing ribs 132 with theexception that in the cathode chamber no horizontal beam is provided.

Embodiment 6

FIG. 9 is an exploded perspective view showing the interior of a ribbedanode chamber in a solid polymer electrolyte fuel cell system accordingto Embodiment 7. A ribbed anode chamber 126A has as a water distributionmeans an electroconductive porous body 136A having a substrate 133A madeof an electroconductive porous material provided with ribs 132A formedintegral to the substrate 133A and defining grooves 134A between anyadjacent two thereof. The ribs 133A arranged parallel to each other andvertical are in contact with the anode, and the substrate 133A ispressed or fixed to an inner side surface of the ribbed anode chamber126A opposing the anode 130. Water is fed to an upper end 133A' of theporous body 136A and spreads through the entire body 136A. A portion ofthe water supplied migrates from the porous body 136A to the anode 130,and then is absorbed by the SPE membrane 124. Excessive water transudesfrom a lower end of the porous body 136A, and is discharged through afirst discharge pipe 46 together with unused fuel gas. Theelectro-conductive porous body is made preferably of a metal. Also,carbon paper having high absorbing properties may be used.

Embodiment 7

FIG. 10 is a perspective view showing ribs of a ribbed anode and a wickin a solid polymer electrolyte fuel cell system according to Embodiment7. A ribbed anode chamber 126 (FIG. 7) has a ribbed plate 131 having asubstrate 133B provided with horizontal grooves and vertical grooves toform many island-like isolated protrusions or ribs 132B. The substrateis fixed to an inner side surface of the ribbed anode chamber opposingthe anode. A wick 136B is provided around the respective ribs 132B toform a network. An upper end 136B' of the wick is arranged in thevicinity of an opening of a water feed pipe 40 (FIG. 7) in the anodechamber 126 (FIG. 7). Water supplied through the water feed pipe 40(FIG. 7) to the upper end of the wick 136B' penetrates or passes throughthe wick 136B and migrates to the anode 130 through the ribs 132B of theribbed anode chamber, and is absorbed by the SPE membrane 124 (FIG. 7).Unabsorbed water or excessive water transudes from a lower end 136B" ofthe wick, and is discharged through the second discharge pipe 58 (FIG.7) together with unreacted fuel gas. The wick 136B is made of finethreads of a fibrous material preferably selected from various naturalfiber, synthetic fiber or metallic fiber, the fine threads being twistedtogether.

Embodiment 8

FIG. 11 is a perspective view showing ribs of a ribbed anode chamber anda hydrophilic band in a solid polymer electrolyte fuel cell systemaccording to Embodiment 8. A ribbed anode chamber 126 (FIG. 7) hastherein a rib plate 133C having a plurality of integral ribs 132Cvertically arranged and parallel to each other to define a groove 134Cbetween any two adjacent ribs 132C. The substrate 133C is pressedagainst or fixed to an inner side surface of the ribbed anode chamber126 opposing the anode 130 (FIG. 9). A hydrophilic band 136C is providedin every other groove 134C. Other particulars of the ribs andhydrophilic bands 136C are substantially the same as those of the ribs32C and hydrophilic bands 36C in Embodiment 4 (FIG. 5). Water fed fromthe water feed pipe 40 (FIG. 9) flows down through a horizontal beam ofthe same structure as the horizontal beam 136 having slits 137 shown inFIG. 8 and is distributed to the plurality of hydrophilic bands 136C. Aportion of the water supplied migrates from the hydrophilic bands 136Cto the ribs 132C sandwiching the respective hydrophilic bands, and isabsorbed by the SPE membrane 124 (FIG. 7). Excessive water transudesfrom respective lower ends of the hydrophilic bands 136C, and isdischarged through the first discharge pipe 46 (FIG. 9). The hydrophilicband 136C may be a rod of a porous metal, a felt or a twisted yarn.

The present invention has been described in detail with respect topreferred embodiments, and it will now be apparent from the foregoing tothose skilled in the art that changes and modifications may be madewithout departing from the invention in its broader aspects, and it isthe invention, therefore, in the appended claims to cover all suchchanges and modifications as fall within the true spirit of theinvention.

What is claimed is:
 1. A solid polymer electrolyte fuel cell systemcomprising:a solid polymer electrolyte membrane; an anode chamberarranged in contact with said solid polymer electrolyte membrane; acathode chamber arranged in contact with said solid polymer electrolytemembrane, said cathode chamber and said anode chamber sandwichingtherebetween said solid polymer electrolyte membrane; a ribbed anodearranged in said anode chamber and having a first surface provided witha plurality of first ribs defining a plurality of first grooves and asecond surface which is flat and in contact with said solid polymerelectrolyte membrane; a ribbed cathode arranged in said cathode chamberand having a first surface provided with a plurality of second ribsdefining a plurality of second grooves and a second surface which isflat and in contact with said solid polymer electrolyte membrane; awater feed pipe for feeding water connected to said anode chamber; afuel gas feed pipe connected to said anode chamber and feeding a fuelgas; a water distribution means for distributing water fed from saidwater feed pipe to said plurality of first ribs, the water distributionmeans being arranged in said anode chamber; a first discharge pipeconnected to said anode chamber and discharging an unused fuel gas andwater; an oxidizer gas feed pipe connected to said cathode chamber andfeeding an oxidizer gas; and a second discharge pipe connected to saidcathode chamber and discharging an unused oxidizer gas and water;whereby said fuel gas passes in said first grooves and said oxidizer gaspasses in said second grooves.
 2. A solid polymer electrolyte fuel cellsystem as claimed in claim 1, wherein said water distribution meanscomprises a beam arranged above said ribbed anode and provided with arestricted passage through which said water from said water feed pipeflows down.
 3. A solid polymer electrolyte fuel cell system as claimedin claim 1, wherein said water distribution means comprises anelectroconductive porous body arranged in contact with said firstsurface of said ribbed anode.
 4. A solid polymer electrolyte fuel cellsystem as claimed in claim 1, wherein said water distribution meanscomprises a network composed of a wick arranged along and between saidfirst ribs of said ribbed anode.
 5. A solid polymer electrolyte fuelcell system as claimed in claim 1, wherein said water distribution meanscomprises a beam arranged above said ribbed anode and provided with arestricted passage through which water flows down and a hydrophilic bandarranged along and embedded in said first ribs of said ribbed anode. 6.A solid polymer electrolyte fuel cell system comprising:a solid polymerelectrolyte membrane; a ribbed anode chamber arranged in contact withsaid solid polymer electrolyte membrane and having a first surfaceprovided with a plurality of first ribs defining a plurality of firstgrooves; a cathode chamber arranged in contact with said solid polymerelectrolyte membrane and having a first surface provided with aplurality of second ribs defining a plurality of second grooves, saidcathode chamber and said anode chamber sandwiching therebetween saidsolid polymer electrolyte membrane; an anode arranged in said anodechamber having a first surface which is flat and in contact with saidsolid polymer electrolyte membrane, and a second surface which is flatand in contact with said first ribs of said ribbed anode chamber; acathode arranged in said cathode chamber and having a first surfacewhich is flat and in contact with said solid polymer electrolytemembrane and a second surface which is flat and in contact with saidsecond ribs of said ribbed cathode chamber; a water feed pipe forfeeding water connected to said ribbed anode chamber; a fuel gas feedpipe connected to said ribbed anode chamber and feeding a fuel gas; awater distribution means for distributing water fed from said water feedpipe to said plurality of first ribs of said ribbed anode chamber, thewater distribution means being arranged in said ribbed anode chamber; afirst discharge pipe connected to said ribbed anode chamber anddischarging an unused fuel gas and water; an oxidizer gas feed pipeconnected to said ribbed cathode chamber and feeding an oxidizer gas;and a second discharge pipe connected to said ribbed cathode chamber anddischarging an unused oxidizer gas and water; whereby said fuel gaspasses in said first grooves and said oxidizer gas passes in said secondgrooves.
 7. A solid polymer electrolyte fuel cell system as claimed inclaim 6, wherein said water distribution means comprises a beam arrangedin an upper portion of said ribbed anode chamber and provided with arestricted passage through which said water from said water feed pipeflows down.
 8. A solid polymer electrolyte fuel cell system as claimedin claim 6, wherein said water distribution means comprises anelectroconductive porous body provided in said first ribs of said ribbedanode chamber.
 9. A solid polymer electrolyte fuel cell system asclaimed in claim 6, wherein said water distribution means comprises anetwork composed of a wick arranged along and between said first ribs ofsaid ribbed anode chamber.
 10. A solid polymer electrolyte fuel cellsystem as claimed in claim 6, wherein said water distribution meanscomprises a beam having a restricted passage for water and a hydrophilicband arranged along and embedded in said first ribs of said ribbed anodechamber.